Direct and Indirect Band Gap Semiconductors

DIRECT AND INDIRECT BAND GAP SEMICONDUCTORS

Based on the composition of semiconductors they are classified as:

(i) Elemental semiconductors (or) indirect bandgap semiconductors

(ii) Compound semiconductors (or) direct band gap semiconductors

(i) Elemental Semiconductors: 

The elemental semiconductor is made of single element from the fourth column elements. Germanium and Silicon are the important examples for elemental semiconductors, these are also known as indirect band gap semiconductors. Here the recombination of an electron from the conduction band with a hole in the valence band takes place via traps. In this process, the phonons are emitted while recombination and they heat the lattice.

(ii) Compound Semiconductors: 

The compound semi- conductors are made by combining the third and fifth column elements (or) second and sixth column elements. GaAs, InP are the important examples for compound semi conductors, these are also known as direct band gap semiconductors. Here the recombination of electron and hole takes place directly and its energy difference is emitted in the form of photons in the visible (or) Infrared range.

Since the life time of the charge carrier is so small, the current amplification is small. Hence these diodes are not suitable for making transistors and ICs, rather they are used in making LEDs and LASER diodes.

Differences between Indirect and Direct band gap Semiconductor